This invention relates generally to fluid dampers for vehicles and more specifically to a blow-off valve assembly.
The invention is specifically applicable to and will be described with particular reference to a blow-off base valve assembly for a twin tube shock absorber. However, those skilled in the art will recognize that the invention may have broader application and conceivably could have application as a piston valve assembly for a twin tube shock absorber or even application to a mono tube shock absorber.
The typical fluid dampers used in vehicle suspensions, such as hydraulic shock absorbers and struts, dissipate energy and filter out road inputs from being transferred to the vehicle""s body and associated passenger compartment. Two common types of vehicle fluid dampers, each having a cylinder and piston, are monotube and twin tube shock absorbers. The preferred embodiment of this invention is directed to twin tube shock absorbers and struts.
Twin tube fluid dampers have a valve body located at an end of the piston commonly referred to as a piston valve and a valve body located at the end of the cylinder commonly referred to as a compression or base valve, and will herein be referred to as a base valve. The piston valve moves towards the base valve during compression and away from the base valve during rebound. The piston and base valve divide the fluid damper into several chambers. In a twin tube damper the chambers are conventionally referred to as a rebound chamber, a compression chamber and a compensation or reservoir chamber (hereinafter referred to as a reservoir chamber).
Two of the more common types of valves used in fluid dampers are deflected-disc type valves and blow-off type valves. With a deflected disc valve, a disc stack is positioned as an obstruction in a fluid flow path. During piston movement, and once sufficient pressure is developed, the disc stack is deflected to provide an increased flow area. The extent to which the disc stack resists deflection assists in determining the damping characteristics of the fluid damper. With a blow-off valve a single valve disc is generally biased by a spring to normally close-off fluid flow passages. Sufficient fluid pressure causes the valve to lift, compressing the spring and providing an increased fluid flow area. Different rate springs and pre-loads allow the valve to blow-off at different pressures thereby regulating damping loads. This invention relates to blow-off type valves.
Typically, both piston and base valves have compression and rebound valve assemblies generally mounted on opposite valve body surfaces. However, in twin tube dampers, the piston valve is generally considered to primarily control the rebound characteristics of the fluid damper while the base valve is generally considered to primarily control the compression characteristics of the fluid damper.
The ride handling characteristics of a damper for a motor vehicle (load versus velocity performance curve) is determined by the individual characteristics of the piston and base valves. For example, during vehicle cornering maneuvers in which the piston undergoes low speed compression, it is desirable for the vehicle to have stiff ride handling characteristics. Conversely, when the vehicle travels over pot holes at relatively high vehicle speeds in which the piston undergoes high speed compression, it is desirable to have soft ride handling characteristics. Different vehicles require different handling characteristics.
As noted, the base valve is the primary control of damping during compression. Typically, fluid dampers are tuned by changing the valve components. Blow-off base valve components which are changed include not only the spring (pre-compression and spring rate) and valve flow-through area which primarily establishes the xe2x80x9csoftxe2x80x9d ride handling characteristic of the vehicle but also the orifice slots in the orifice disc which primarily sets the stiffness of the fluid damper for vehicle cornering. Additionally, the rebound components of the blow-off valve may also have to be changed.
Currently, the components are individually assembled onto a valve body which has a castellated end edge configuration for securement in the formed and rounded bottom end of the damper cylinder. Assembling the individual components onto the valve body is time consuming. The assembly process could lead, as in any assembly process, to error such as an inadvertent spring pre-compression force if fastener type arrangements are used to set the pre-compression force. At the same time, the valve assemblies are sophisticated assemblies with what may be viewed as minor structural changes producing substantial changes in valve performance. The potential exists for a component of one valve to be inadvertently assembled into another valve. Additionally, different diameter cylinders require different valve components.
Accordingly, it is one of the major objectives of the invention to provide a modularized fluid damper blow-off base valve assembly to alleviate the problems noted above.
This object along with other features and advantages of the invention is achieved in a base valve for regulating flow of fluid through a twin tube fluid vehicle damper having inner and outer damper tubes. The base valve includes a valve body having i) a cylindrical outer wall portion sealed to an end of the inner damper tube, ii) a rebound surface adjacent one end of the outer wall portion and a compression surface adjacent the opposite end of the outer wall portion, iii) a central opening therein between the compression and rebound surfaces, and iv) a return opening therein between the compression and rebound surfaces spaced radially outward from the central opening. A low speed compression orifice disc or bleed disc is provided to cover the rebound opening and to regulate low speed control and it has at least one orifice in fluid communication with the rebound opening. A modular valve assembly is seated within and extends through the central opening. The modular blow-off assembly includes a tubular valve cage having a blow-off valve opening extending over a central area of the blow-off assembly for a compression fluid flow therethrough. The modular assembly further includes an annular blow-off valve seat circumscribing the blow-off valve opening and a helical spring biasing the valve seat to close the blow-off opening so that compression flow of fluid may be set at a desired blow-off pressure and rate by simply selecting blow-off valve seats and spring preload and rate which are assembled and contained within the valve cage as a single unit.
In accordance with another aspect of the invention, the modular blow-off assembly includes the tubular valve cage having i) a tubular member seated and extending through the valve body""s central opening at an upper end thereof with the tubular member""s upper end having the blow-off valve opening therein, ii) a spring retainer adjacent a bottom end of the tubular member extending radially inward, iii) a valve stem having a seat surface adjacent the blow-off opening for sealing and unsealing the blow-off opening and a guide surface extending from the seat surface and iv) the spring positioned between the spring retainer and the seat surface of the valve stem to bias the blow-off valve seat into sealing contact with the blow-off valve opening. Because the valve cage contains the blow-off valve opening within the valve cage, differently sized dampers, i.e., 25-46 mm, having different diameter valve bodies but commonly sized central openings can utilize common valve cages and, depending on vehicle application, identical cage components such as the tubular member or the spring retainer are possible.
In accordance with another feature of the invention, the upper end of the tubular member has a shoulder extending radially outward from the central opening of the valve body. The bleed disc and an intake disc functioning as a check valve are in the shape of a washer and are positioned on the tubular member centered about the blow-off valve opening. A leaf spring is provided in the shape of a washer centered about the tubular member and bent with flats to contact the underside of the shoulder and exert a bias against the intake and bleed discs whereby desired low speed compression bleed damping rates can be obtained by simply interchanging bleed discs with different orifices in the modular blow-off valve assembly and/or desired rebound characteristics can be similarly obtained by interchanging or adding higher leaf spring rates.
In accordance with another aspect of the invention, a method for assembling a base valve having reset fluid flow characteristics into an end of an inner tube of twin tube vehicle damper is provided which includes the steps of:
a) providing a cylindrical valve body having an annular compression surface at one side thereof and an annular rebound surface on its opposite side with the compression and rebound surfaces extending radially outward and blending into a cylindrical castellated end wall portion and the valve body having at least one generally central opening therethrough and at least one rebound opening extending therethrough spaced radially outward from the central opening;
b) pressing the cylindrical end wall portion into an end of the inner tube to establish a seal between the inner tube and the valve body;
c) providing a tubular valve cage having a tubular member with an upper end and a lower end, a spring retainer, a helical spring, and a valve stem with the upper end of the valve cage and the valve stem forming a valve seat therebetween for closing and opening a valve opening formed in the valve cages"" upper end;
d) placing the valve stem into the valve cage followed by the spring with one spring end contacting the stem followed by compressing or predeflecting the spring retainer into a groove formed at a set distance at the lower end of the valve cage to form a modular valve cage assembly; and,
e) inserting the modular valve cage assembly into the valve body in a sealed manner by press fitting the outer surface of the tubular member into the valve body""s central opening whereby a blow-off valve is assembled into the damper.
In accordance with a specific aspect of the inventive assembly aspects of the invention, the assembly process includes the additional steps of:
f) providing a bleed disc having at least one orifice in fluid communication with the rebound opening, at least one intake disc and a leaf spring disc with all of the discs in the shape of washers and each having an inside diameter greater than the outside diameter of the central opening and an outside diameter greater than the radial distance of the rebound opening; and,
g) prior to step (e), when placing the disc over the tubular member with the leaf spring contacting the underside of the shoulder and completing step (e) by pressing the tubular body into the central opening of the valve body a distance sufficient only to set a predetermined spring biasing force on the intake and orifice discs whereby the rebound characteristics of the valve, specifically the pre-compression spring force, are established, in part, by the assembly of the modular valve assembly.
In general summary, various objects, features and advantages of the invention include one or more or any combination of the following with respect to the base valve of a twin tube vehicle damper:
i) the expense of the base valve is reduced;
ii) the installation of the base valve is simplified;
iii) it is easier to optimize the design of a base valve to meet customer specific damper requirements for various vehicle platforms; and/or,
iv) it is possible to provide a wider range of damper performance with a common construction than what was heretofore possible.
It should also be noted that while the invention was developed for, and is specifically applied to, the base valve of a twin tube hydraulic damper, it is recognized and therefor a feature or advantage of the invention, that the modular valve concepts disclosed herein can have application to damper valves other than the base valve and, specifically, conceivably could be applied as a piston blow-off valve or a valve used in mono-tube dampers.
Similarly, and again noting that while the modular valve was developed as a twin tube damper based valve which primarily controls compression, the modular valve assembly has conceptual application for digressive rebound valve characteristics in a modular valve assembly for use in any damper valve.